Changing the shape and colour of keratinous fibres, in particular hair, constitutes an important area of modern cosmetics. By employing this, the appearance of the hair as well as the latest fashion trends and also an individual's aspirations can be harmonized. In order to change the hair colour, the person skilled in the art will be aware of a variety of colouring systems which will satisfy the various requirements. For permanent, intense colours with good colour fastness and good grey coverage, oxidative dyes are usually used. Colorants of this type usually contain oxidative dye precursors, known as developer components and coupler components, which together produce the actual dyes under the influence of oxidizing agents such as hydrogen peroxide, for example. Oxidative dyes are distinguished by outstanding, long-lasting colour results, but on the downside are linked to a certain amount of damage to the hair.
If the consumer wishes to reduce damage to the hair or only to change the hair colour temporarily, then they may wish to turn to colorants which are based on direct dyes. Here, fully-formed dyes diffuse out of the colorant into the hair fibres. Compared with oxidative hair colouring, the colours obtained with direct dyes are less long-lasting and wash out more quickly. In addition, the grey coverage which can be obtained with direct dyes is generally in need of improvement. However, the advantage is that colouring with direct dyes causes less damage to the hair.
The person skilled in the art will divide direct dyes into various dye classes as a function of the desired colour result. The direct dyes which are known in the art belong, for example, to the nitro dye, anthraquinone dye, azo dye, triarylmethane dye or methine dye categories. All of these categories of dyes are intended to satisfy a specific set of requirements for use in the cosmetics arena. Thus, direct dyes deliver an intense colour result and superlative colour fastness. Environmental influences should affect the colour result obtained with direct dyes to the least extent possible, i.e. the dyes should, for example, possess good fastness to washing, light and rubbing. The influence of chemicals to which the keratinous fibres could be exposed following the colour process (for example permanent waving), should also change the colour result to the least possible extent.
Direct dyes can be divided into anionic, cationic and non-ionic direct dyes. In cosmetic compositions, these interact to varying degrees with the remaining components of the compositions. In this regard, surface-active substances such as surfactants or emulsifying agents which are contained in them have a major influence. In the cosmetic compositions, they are meant to release contaminants from the keratinous fibres and/or to emulsify components of the composition itself. However, depending on the choice of the surface-active substance, this may also lead to interactions between them and the direct dyes, whereupon the colour result could be significantly impaired compared with agents which contain no surface-active substances.
Surfactants or emulsifying agents are amphiphilic (bifunctional) compounds which include at least one hydrophobic and at least one hydrophilic portion of the molecule. The hydrophobic residue is usually a hydrocarbon chain. The hydrophilic residue may have a negative charge, a positive charge, a negative and a positive charge or no charge, depending on the type of surfactant.
In anionic surfactants, the hydrophilic portion of the molecule comprises at least one hydrophilic head group with a negative charge. Anionic surfactants exclusively contain negative charges. “Cationic surfactants” should be understood to mean surfactants, i.e. surface-active substances, which respectively have one or more positive charges. Cationic surfactants exclusively contain positive charges.
Zwitterionic (amphoteric) surfactants comprise, in the hydrophilic portion of the molecule, at least one group with a negative charge and at least one group with a positive charge. These are spatially separated from each other and are close to each other, whereupon the surfactant is electrically neutral overall.
Moreover, non-ionic (non-ionogenic) surfactants exist which are distinguished by the absence of electric charges in the molecules.
The person skilled in the art has long been aware that many surfactants can significantly impair the colour uptake of direct dyes onto keratinous fibres. Not all types of surfactants are compatible with all types of direct dyes. The colour uptake of direct dyes is to a large extent dependent on the type of surfactants and the type of the dyes. Anionic surfactants in this regard have a particular negative effect on the colour uptake of non-ionic and cationic dyes, as well as on anionic dyes. Cationic surfactants, on the other hand, have a particular negative impact on the colour uptake of non-ionic and anionic dyes, as well as on cationic dyes.
In order to overcome this problem, until now, as a rule, only compositions in which the dye and the surfactant have been precisely matched to each other are used. It is thus not possible to use any dye with any surfactant or to combine several dyes together in any manner in order to obtain the desired shade.
Correspondingly, the prior art discloses various such compositions. EP 1 935 455 A1 discloses a composition comprising a direct dye in combination with at least one bioheteropolysaccharide, at least one cationic surfactant and at least one amphoteric surfactant. WO 2013/041485 A2 describes a composition comprising at least one dye, for example a direct dye, at least one fat in the form of a long-chain dialkylcarbonate or dialkenylcarbonate, at least one alkylpolyglycoside as well as at least one cationic and/or amphoteric polymer. Examples of cleaning compositions with various combinations of surfactants are provided in WO 2016/040158 A1, WO 2013/082413 A1 and WO 2014/149019 A1. None of those compositions is particularly suitable for improving the colour distribution of direct dyes.
Conventional surfactant-containing colorants with direct dyes (toning shampoos) are usually optimized for either the best colouring properties or for the best cleaning properties or for the best foam formation. The range of mutually combinable direct colours and surfactants is limited, and so the flexibility of possible dye combinations with direct dyes is limited.
Thus, the objective of the present disclosure is to provide a surfactant-containing colorant based on direct dyes which is compatible with a wide variety of different direct dyes and which ensures good colour uptake. Furthermore, the agent should allow for as varied a range of colours, chromaticity and colour intensity as possible.
Finally, the agent should also exhibit good cleaning action and good foam formation properties and be easy to use.